 Toutatis imaged byChang'e 2 during its flyby | |
| Discovery[1] | |
|---|---|
| Discovered by | Christian Pollas |
| Discovery site | Caussols |
| Discovery date | 4 January 1989 |
| Designations | |
| (4179) Toutatis | |
| Pronunciation | /taʊˈteɪtɪs/[citation needed] |
Named after | Toutatis(Celtic mythology)[2] |
| |
| Adjectives | Toutatian[4] |
| Orbital characteristics[3] | |
| Epoch 27 November 2008 (JD 2454797.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 83.29 yr (30,422 days) |
| Earliestprecovery date | 10 February 1934 |
| Aphelion | 4.1242 AU |
| Perihelion | 0.9399 AU |
| 2.5321 AU | |
| Eccentricity | 0.6288 |
| 4.03 yr (1,472 days) | |
| 5.1220° | |
| 0° 14m 40.56s / day | |
| Inclination | 0.4460° |
| 124.30° | |
| 278.75° | |
| Earth MOID | 0.0064 AU (2.5 LD) |
| Physical characteristics | |
| Dimensions | |
| 2.45 km[6] | |
| Mass | 1.9×1013 kg[7] |
Meandensity | 2.5 g/cm3[7] |
| 176 h (7.3 d)[8] | |
| 0.13[3] | |
| Sk(SMASSII)[3] | |
| 8.8–22.4[9][10] | |
| 15.30[3] | |
4179 Toutatis (provisional designation1989 AC) is an elongated, stonyasteroid andslow rotator,[11] classified as anear-Earth object andpotentially hazardous asteroid of theApollo asteroid group, approximately 2.5 kilometers in diameter. Discovered by French astronomerChristian Pollas atCaussols in 1989, the asteroid was named afterToutatis from Celtic mythology.[1][2]
Toutatis is also aMars-crosser asteroid with achaotic orbit produced by a 3:1resonance with the planetJupiter, a 1:4 resonance with the planetEarth, and frequent close approaches to theterrestrial planets, including Earth.[12] In December 2012, Toutatis passed within about 18lunar distances of Earth. The Chinese lunar probeChang'e 2 flew by the asteroid at a distance of 3.2 kilometers and a relative velocity of 10.73 km/s.[13] Toutatis approached Earth again in 2016, but will not make another notably close approach until 2069.[14]
Toutatis was first sighted on 10 February 1934, as object 1934 CT, but lost soon afterwards.[15] It remained alost asteroid for several decades until it was rediscovered on 4 January 1989 byFrenchastronomerChristian Pollas, and was named after theCeltic god of tribal protectionToutatis (Teutates). The name of this god is very familiar inFrance due to thecatchphrasePar Toutatis! by the Gauls in thecomicsAsterix.[16]
The spectral properties suggest that this is anS-type, or stony asteroid, consisting primarily ofsilicates. It has a moderateBond albedo of 0.13.[3]Radar imagery shows that Toutatis is a highly irregular body consisting of two distinct lobes, with maximum widths of about 4.6 km and 2.4 km, respectively. It is hypothesized that Toutatis formed from two originally separate bodies which coalesced at some point (acontact binary), with the resultant asteroid being compared to arubble pile.
Its rotation combines two separate periodic motions into a non-periodic result; to someone on the surface of Toutatis, theSun would seem to rise and set in apparently random locations and at random times at the asteroid's horizon. It has arotation period around its long axis (Pψ) of 5.38 days. This long axis isprecessing with a period (Pφ) of 7.38 days.[17] The asteroid may have lost most of its original angular momentum and entered into this tumbling motion as a result of theYORP effect.[18]
With asemimajor axis of 2.5294 AU, or roughly 2.5 times the distance between Earth and the Sun, Toutatis has a 3:1orbital resonance with Jupiter and a near-1:4 resonance with Earth making it a member of theAlinda asteroid group.[12][19] It thus completes one orbit around the Sun for every 4.02 annual orbits of Earth. Thegravitational perturbations caused by frequent close approaches to the terrestrial planets lead tochaotic behavior in the orbit of Toutatis,[20] making precise long-term predictions of its location progressively inaccurate over time.[20] Estimates in 1993 put theLyapunov time horizon for predictability at around 50 years,[20] after which the uncertainty region becomes larger with each close approach to a planet. Without theperturbations from the terrestrial planets the Lyapunov time would be close to 10,000 years.[20] The initial observations that showed its chaotic behavior were made byWiśniewski.[21]
The lowinclination (0.47°) of the orbit allows frequenttransits, where the inner planets Mercury, Venus, Earth, and Mars can appear to cross the Sun as seen from the perspective of Toutatis. Earth did this in January 2009, July 2012, July 2016 and 2020.[22]
| Close approaches[14] | ||
|---|---|---|
| Year | AU | LD |
| 1985 | 0.28 | 109 |
| 1988 | 0.12 | 45 |
| 1992 | 0.02 | 9 |
| 1996 | 0.03 | 14 |
| 2000 | 0.07 | 29 |
| 2004 | 0.01 | 4 |
| 2008 | 0.05 | 20 |
| 2012 | 0.05 | 18 |
| 2016 | 0.25 | 98 |
| 2065 | 0.36 | 142 |
| 2069 | 0.02 | 8 |
Toutatis makes frequent close approaches to Earth, with a currently minimum possible distance (EarthMOID) of just 0.006 AU (2.3 times as far as theMoon).[3] The approach on 29 September 2004 was particularly close, at 0.0104 AU[23] (within 4lunar distances) from Earth, presenting a good opportunity for observation, with Toutatis having anapparent magnitude of 8.8 at its brightest.[9] A close approach of 0.0502 AU (7,510,000 km; 4,670,000 mi) happened on 9 November 2008.[14][23] The most recent close approach was on 12 December 2012, at a distance of 0.046 AU (6,900,000 km; 4,300,000 mi),[14][23] with a magnitude of 10.7.[24] At magnitude 10.7, Toutatis was not visible to thenaked eye, but just visible to experienced observers using high-endbinoculars. During the 2012 encounter Toutatis was recovered on 21 May 2012, by theSiding Spring Survey atapparent magnitude 18.9.[25] A close approach will be 5 November 2069, at 0.01985 AU (2,970,000 km).[14]
Given that Toutatis makes many close approaches to Earth, such as in 1992, 1996, 2000, 2004, 2008, 2012, and 2016, it is listed as apotentially hazardous object.[14] With anuncertainty parameter of 0,[3] the orbit of Toutatis is very well determined for the next few hundred years.[14] The probability of the orbit intersecting Earth is essentially zero for at least the next six centuries.[26] The likelihood of collision in the distant future is considered to be very small.[27] As a planet-crossing asteroid, Toutatis is likely to be ejected from the inner Solar System within a few million years. In 2004 achain e-mail falsely claimed that Toutatis had a 63% chance of impacting Earth then. In fact, Toutatis passed by at 1.5 million kilometres, or about four Earth–Moon distances, as predicted.[28]
In 2006 Toutatis came closer than 2 AU to Jupiter; its orbit lies inside of Jupiter's.[14] In the 2100s, it will approach Jupiter many times at a similar distance.[14]
| PHA | Date | Approach distance (lunar dist.) | Abs. mag (H) | Diameter (C) (m) | Ref (D) | ||
|---|---|---|---|---|---|---|---|
| Nomi- nal(B) | Mini- mum | Maxi- mum | |||||
| (33342) 1998 WT24 | 1908-12-16 | 3.542 | 3.537 | 3.547 | 17.9 | 556–1795 | data |
| (458732) 2011 MD5 | 1918-09-17 | 0.911 | 0.909 | 0.913 | 17.9 | 556–1795 | data |
| (7482) 1994 PC1 | 1933-01-17 | 2.927 | 2.927 | 2.928 | 16.8 | 749–1357 | data |
| 69230 Hermes | 1937-10-30 | 1.926 | 1.926 | 1.927 | 17.5 | 668–2158 | data |
| 69230 Hermes | 1942-04-26 | 1.651 | 1.651 | 1.651 | 17.5 | 668–2158 | data |
| (137108) 1999 AN10 | 1946-08-07 | 2.432 | 2.429 | 2.435 | 17.9 | 556–1795 | data |
| (33342) 1998 WT24 | 1956-12-16 | 3.523 | 3.523 | 3.523 | 17.9 | 556–1795 | data |
| (163243) 2002 FB3 | 1961-04-12 | 4.903 | 4.900 | 4.906 | 16.4 | 1669–1695 | data |
| (192642) 1999 RD32 | 1969-08-27 | 3.627 | 3.625 | 3.630 | 16.3 | 1161–3750 | data |
| (143651) 2003 QO104 | 1981-05-18 | 2.761 | 2.760 | 2.761 | 16.0 | 1333–4306 | data |
| 2017 CH1 | 1992-06-05 | 4.691 | 3.391 | 6.037 | 17.9 | 556–1795 | data |
| (170086) 2002 XR14 | 1995-06-24 | 4.259 | 4.259 | 4.260 | 18.0 | 531–1714 | data |
| (33342) 1998 WT24 | 2001-12-16 | 4.859 | 4.859 | 4.859 | 17.9 | 556–1795 | data |
| 4179 Toutatis | 2004-09-29 | 4.031 | 4.031 | 4.031 | 15.3 | 2440–2450 | data |
| 2014 JO25 | 2017-04-19 | 4.573 | 4.573 | 4.573 | 17.8 | 582–1879 | data |
| (137108) 1999 AN10 | 2027-08-07 | 1.014 | 1.010 | 1.019 | 17.9 | 556–1795 | data |
| (35396) 1997 XF11 | 2028-10-26 | 2.417 | 2.417 | 2.418 | 16.9 | 881–2845 | data |
| (154276) 2002 SY50 | 2071-10-30 | 3.415 | 3.412 | 3.418 | 17.6 | 714–1406 | data |
| (164121) 2003 YT1 | 2073-04-29 | 4.409 | 4.409 | 4.409 | 16.2 | 1167–2267 | data |
| (385343) 2002 LV | 2076-08-04 | 4.184 | 4.183 | 4.185 | 16.6 | 1011–3266 | data |
| (52768) 1998 OR2 | 2079-04-16 | 4.611 | 4.611 | 4.612 | 15.8 | 1462–4721 | data |
| (33342) 1998 WT24 | 2099-12-18 | 4.919 | 4.919 | 4.919 | 17.9 | 556–1795 | data |
| (85182) 1991 AQ | 2130-01-27 | 4.140 | 4.139 | 4.141 | 17.1 | 1100 | data |
| 314082 Dryope | 2186-07-16 | 3.709 | 2.996 | 4.786 | 17.5 | 668–2158 | data |
| (137126) 1999 CF9 | 2192-08-21 | 4.970 | 4.967 | 4.973 | 18.0 | 531–1714 | data |
| (290772) 2005 VC | 2198-05-05 | 1.951 | 1.791 | 2.134 | 17.6 | 638–2061 | data |
| (A) List includes near-Earth approaches of less than 5lunar distances (LD) of objects withH brighter than 18. (B)Nominal geocentric distance from the Earth's center to the object's center (Earth radius≈0.017 LD). (C) Diameter: estimated, theoretical mean-diameter based onH andalbedo range between X and Y. (D) Reference: data source from theJPL SBDB, withAU converted into LD (1 AU≈390 LD) (E) Color codes: unobserved at close approach observed during close approach upcoming approaches | |||||||
Large amounts of data of Toutatis were obtained duringChang'e 2's flyby. Toutatis is not a monolith, but most likely a coalescence of shattered fragments. This bifurcated asteroid is shown to be mainly consisting of a head (small lobe) and a body (large lobe). The two major parts are not round in shape, and their surfaces have a number of large facets. In comparison with radar models, the proximate observations from Chang'e 2's flyby have revealed several remarkable discoveries concerning Toutatis, among which the presence of the giant basin at the big end appears to be one of the most compelling geological features, and the sharply perpendicular silhouette in the neck region that connects the head and body is also quite novel. A large number of boulders and several short linear structures are also apparent on the surface.[5]
The giant basin at the big end of Toutatis has a diameter of ~805 m, suggesting that one or more impactors may have collided with it there. The most significant feature is the ridge around the largest basin. The wall of this basin has a relatively high density of lineaments, some of which seem to be concentric to the basin. These ridges are indicative of an internal structure of small bodies and most of the ridges near the largest basin at the big end are most likely related to the huge stress energy during impact.[5]
Toutatis has been observed with radar imaging from theArecibo Observatory and theGoldstone Solar System Radar during the asteroid's prior Earth flybys in 1992, 1996, 2000, 2004, and 2008. It was also observed with radar during the December 2012 flyby and observed more distant flyby with radar in December 2016.[29] After 2016, Toutatis will not pass close to Earth again until 2069.[14]
Resolution of the radar images is as fine as 3.75 m per pixel,[30] providing data to model Toutatis's shape and spin state.
The Chinese lunar probeChang'e 2 departed from the Sun–Earth L2 point in April 2012[31] and made a flyby of Toutatis on 13 December 2012, with closest approach being 3.2 kilometers and a relative velocity of 10.73 km/s, when Toutatis was near its closest approach to Earth.[13][32][33] It took several pictures of the asteroid, revealing it to be a dusty red/orange color.
